Despite security screening of all passengers prior to boarding an aircraft, and security surveillance measures carried out in airports, it still remains possible for terrorists or hijackers, even carrying weapons of various types, to board a passenger transport aircraft. Once on board, a terrorist or hijacker has relatively easy access to the entire passenger cabin space as well as the cockpit, and can therefore rather easily take over control of the aircraft. Conventional commercial aircraft include very little, or essentially no, effective measures to prevent or at least hinder the takeover of the aircraft by a terrorist or hijacker.
Increased security measures on the ground will presumably make it more difficult for terrorists to smuggle diverse weapons on board an aircraft, for use in the hijacking of the aircraft or other violent or aggressive actions. Nonetheless, it seems that a group of terrorists with close combat or hand-to-hand combat training may be able to board and commandeer a conventional aircraft, even without generally recognizable weapons, such as guns, knives, explosives, or the like. Instead, such trained terrorists can use common everyday items of clothing or the like (e.g. a belt, shoelaces, writing pens, or the like) to threaten, restrain, injure, or even kill members of the flight crew or passengers and thereby forcefully and violently gain control of the aircraft.
A conventional countermeasure against such terrorist or hijacking activities involves placing armed security personnel, so-called “sky marshals”, on commercial aircraft flights. There has also been public discussion about training and arming pilots or other members of the flight crew. Such security measures, however, are based on the assumption that there will necessarily be a violent armed conflict involving the discharge of firearms and the like between the terrorists and the armed crew members or sky marshals. That in itself is a dangerous situation, which should preferably be avoided, because it can easily, accidentally lead to the injury or death of innocent bystander passengers, as well as critical damage to the aircraft airframe structure or onboard systems of the aircraft, which means a high risk of a crash of the aircraft, even if the terrorists can be subdued.